Any idea what this is about?

I have 8 RIR hens and 4 RIR roosters. They're about 5 months old and have been together from birth.

We have a 12x18 shed that we've tweaked into a house with laying boxes, roosts for night time, etc.

Attached to the house is a large run - probably 500 sq ft.

The chickens have always had full run of the house and the outside run except at night when they're closed up in the house for protection from predators.

Yesterday one of our roosters started an odd behavior - he won't leave the house. He's not injured and doesn't appear to be sick, he just won't leave the house. Even when I've taken goodies out to the run for extra feed (zucchini, etc. for treats) he stays inside while the others grab for every nugget. I've even gone so far as carry him out to the run to see if the other roosters were picking on him or something, but they just ignored him as they always have. Yet he RAN back inside.

i have a silkie that got chased down by my dog yesterday ... dog didn't hurt it ... just slobbered on it a bit ... it took a while for that silkie to come back out of the run and into the yard ... could be something similar

One of my roos stays indoors most of the time -- since one day when he went out he was jumped on, flogged, and dominated by another roo. Once in a great while he will come out, but he just sits in the door and watches most of the time. Some of his girls always stay in with him.